Various instruments are known in the art for removing various objects from the body. For example, such instruments are used for removal of stones such as kidney stones, gallstones, and the like from various sites along the urinary tract of a patient's body. Retrieval devices are also widely used for removing foreign articles from the vascular system of a patient. In such a case, examples of the foreign articles include vena cava filters and parts of medical devices, such as catheters, guidewires, cardiac leads, etc., which may break and become detached during medical procedures.
Some types of these instruments employ a retrieval collapsible wire basket arranged within a flexible catheter formed as a tubular sheath adapted to penetrate body passages to reach the location from where the object is to be evacuated (see, for example U.S. Pat. Nos. 5,658,296; 6,168,603; and 6,491,698 to Bates et. al.). The basket and the sheath can move relative to each other to open and close the basket. The basket consists of flexible wires and is made of a material capable to provide the basket with elasticity. The wires are bound together in the vicinity of a basket proximal end as well as at a basket distal end. Depending on the manipulation, the basket may either retract inside the sheath, to allow penetration of the catheter via a passage, or protract from the catheter. In the protracted position, the basket is open, due to the elasticity of the wire material, and forms a cage to thus allow entrance of the object into the basket through the open spaces left between its adjacent wires. Further retraction of the basket into the sheath results in the cage collapsing and entrapping the object in the basket. Removal of the catheter will enable the whole device to be removed from the body organ together with the object immobilized within the basket. During an operation, the operator moves the catheter behind the object to be extracted, and then protracts the basket from the catheter. Once the basket is protracted, it opens (due to its resiliency), and is ready for receiving the object to be entrapped therein. The operator pulls the catheter together with the basket until it entraps the object, and then extracts the entrapped object from the body.
Another type of retrieval device includes miniaturized grasping forceps configured for grasping the foreign body anywhere along its length. For example, U.S. Pat. Nos. 5,300,086 to Gory et al.; 5,944,728 to Bates; 6,331,183 to Suon; and 6,506,209 to Teruo describe various extractors that have a sheath and a grabber comprised of a plurality of catching legs that are unattached at a distal end of the grabber and joined at a proximal base of the grabber. The legs are movable relative to the sheath to achieve a contracted position within the sheath and an extended position outside of the sheath in the form of an open grasper. The distal ends of the legs are farther apart from each other when the grabber is in the open position than when in the closed position. One drawback in the use of grasping forceps is associated with the fact that if the body passage is narrow, it may offer only limited space for the forceps to open and close. Moreover, the catching legs are typically formed of elastic wires with insufficient rigidity to reliably hold the foreign body. Thus, the legs may deform and drop the foreign object during operation.
Another known type of retrieval device is a snare configured as a single distal loop which is positioned over a free end of the foreign body, and which is contracted and tightened around it (see, for example, U.S. Pat. Nos. 1,722,474 to Langbein; 3,828,790 to Curtiss; 4,326,530 to Fleury; 5,171,314 to Dulebohn; 5,171,233 to Amplatz et al.; and 5,417,684 to Jackson et al.).
For example, U.S. Pat. No. 5,171,233 to Amplatz et al. describes a vascular snare that consists of a super-elastic nitinol cable with a single-formed loop. Because of the snare's super elastic construction, the loop can be contracted for passage through a small sheath and yet automatically open into its original, unrestrained configuration upon emerging from the distal tip of the sheath. The loop is formed at approximately 90 degrees to the cable, and this presents the full area of the loop in a distal direction, enhancing the ability to slip the loop over a foreign body and ensnare it by closing the loop with a small sheath. The foreign body is removed from the body passage by withdrawing the device into a guiding catheter. One of the drawbacks of single loop snares is poor cross sectional lumen coverage that requires skilled manipulation to capture the desired object.
In an attempt to provide a snare with improved cross sectional vessel coverage, multi loop snares have been developed. These snares include loops which are joined only at their proximal ends to a manipulation shaft, and otherwise are not joined at any point between the shaft and the distal ends of the loops.
For example, U.S. Pat. No. 5,098,440 to Hillstead describes a method and apparatus for retrieving an object such as a stent from a subject. A catheter supports two wire loops that can be manipulated from outside the subject to engage the object. By manipulating the catheter and the wire loops, the object can be captured and drawn inside a guide catheter through which the catheter is inserted. The catheter and attached stent can then be pulled from the subject.
U.S. Pat. No. 6,099,534 to Bates describes a snare formed of two or more loops. The snare opens and closes for end-entrapping an object and is strengthened by support members that interconnect the loops. The captured object can be released from the snare by opening the loops.
It should be noted that the snares described by Hillstead and Bates include loops which are joined only at their proximal ends to a manipulation shaft, and otherwise are not joined at any point between the shaft and the distal ends of the loops. Such multi-loop snares provide the advantage over single loop snares owing to enhanced cross sectional vessel coverage, and possibility to bring together the free distal ends of the loops and thereby to engage multiple surfaces of an intravascular medical device to be removed. The drawback of the multi-loop snares having loops attached at only the proximal ends is that the relative geometry of the free loops is difficult to maintain due to the lack of dilatative strength. These snares are not resistive to forces countering snare opening. Because the relative position of the loops can change, both within a catheter and within a body tract, the loops can actually become displaced and/or entangled, thus preventing the snare from opening during operation.
This problem is addressed in U.S. Pat. No. 6,458,145 to Ravenscroft et al., which describes an intravascular snare that includes a central shaft with a plurality of loops attached to the shaft at their proximal ends. In order to strengthen the construction, the loops are connected together at joinder points located between the distal and proximal ends of the loops to maintain the relative geometry of the loops in both an expanded and compressed condition. Specifically, each side of each loop in the snare of U.S. Pat. No. 6,458,145 is connected to a side of an adjacent loop at only one joinder point. Although this can strengthen the construction, the structural rigidity and dilatation ability of the snare can still be not sufficient to reliably hold the foreign body.
U.S. Pat. No. 2008/0086149A to Diamant at. al. describes a retrieval snare for entrapping and retaining a foreign object located in a body and a method for manufacturing of the snare are provided. The snare comprises a structure having a proximal portion and a distal portion and includes a plurality of filaments. The filaments extend from an end of the proximal portion towards the distal portion and return to the end of the proximal portion to form a plurality of loops. The loops are not interconnected at the distal portion, but each side of each loop is connected to a side of an adjacent loop in the proximal portion at more than one point, thereby providing structural rigidity and dilatation ability to the snare.
Another known type of technique for removing objects from a body utilizes a suction catheter to a foreign object in a body cavity, for example, to a detached blood clot (thromboembolism) that travels through the bloodstream and lodges so as to obstruct or occlude a blood vessel. The technique involves advancing a suction catheter to the thromboembolism with the goal of removing it via aspiration (i.e. negative pressure).
Many exiting aspiration catheters, for example, export aspiration catheters from Medtronic, pronto extraction catheters manufactured by Vascular Solutions, etc. are all in the form of an aspiration tube, with a dimension sufficient for insertion through a guiding catheter. Thus, the distal tip of such catheters is usually narrow and it does not enable aspiration of large thrombus clots.
For example, U.S. Pat. Appl. Pub. No. US2009/0270808A to Juan-Pablo Mas at. al. describes an aspiration catheter in which rapid withdrawal of a piston disposed within a distal region of a catheter lumen creates a sudden pressure drop for ingestion of intravascular matter into the catheter lumen through a distal port while avoiding large losses of suction common with catheters having long aspiration lumens. One of the disadvantages of this device is associated with the fact that it cannot entrap an object located in a patient's body. Thus, when performing thrombus aspiration, it is not rare that at the end of the aspiration action, and while withdrawing the aspiration catheter, a clot is still attached to the distal tip. The physician is usually not aware of that and can hardly notice this under imaging. This is very dangerous, as the clot can be detached from the catheter and block a normal artery or worse, cause pulmonary or brain embolism. Moreover, such device can be mainly effective with relatively soft thrombus-emboli.
To enhance effectiveness of aspiration techniques, U.S. Pat. Appl. Pub. No. 2006/0058838A to Bose at. al. describes an apparatus for withdrawing thromboembolic material from a blood vessel that includes an aspiration device having an elongate member together with a receiver on a distal portion of the elongate member. The receiver is formed of a plurality of structural members arranged to form a sleeve having a central lumen. A plurality of the structural members comprises engaging elements including apex regions extending into the central lumen. Although the apparatus described in US2006/0058838A provides a possibility to receive a foreign object located in a body, the configuration of the receiver does not allows entrapping and retaining the foreign object within the receiver. Thus, the foreign object can easily escape from the receiver, and the apparatus can drop the object during operation.